Hand-held and hand-operated printing devices with an ink-jet print-head are known through various documents.
U.S. Pat. No. 5,927,872 to Yamada discloses a system and a method of printing an image represented by a frame of image data utilizing a hand-held printer having optical sensor means for tracking positions of the hand-held printer relative to the surface of a print medium during a printing process. It is monitored in real time using navigation information generated by the optical sensor.
Each optical sensor comprises an array of opto-electronic elements to capture images of the surface of a print medium at fixed time intervals. Preferably, the optical sensor means can detect slight pattern variations on the print medium, such as paper fibers or illumination pattern formed by highly reflective surface features and shadowed areas between raised surface features. These features can then be used as references for determining the position and the relative movement of the hand-held printer. During the printing process, the printed portions of the image can also be used as reference positions by the hand-held printer.
In the preferred embodiment, the hand-held printer contains a navigation processor and a printer driver. Using the printer driver, the navigation processor drives the hand-held printer to print segments of the image onto a print medium as the hand-held printer travels across the print medium during a printing process. Each segment of the image is printed onto a particular location on the print medium to form a composite of the image.
In the U.S. Pat. No. 6,233,368 B1 to Badyal et al it is taught a CMOS digital integrated circuit (IC) chip on which an image is captured, digitized, and then processed on-chip in substantially the digital domain.
A preferred embodiment comprises imaging circuitry including a photo cell array for capturing an image and generating a representative analog signal, conversion circuitry including an n-bit successive approximation register (SAR) analog-to-digital convertor for converting the analog signal to a corresponding digital signal, filter circuitry including a spatial filter for edge and contrast enhancement of the corresponding image, compression circuitry for reducing the digital signal storage needs, correlation circuitry for processing the digital signal to generate a result surface on which a minima resides representing a best fit image displacement between the captured image and previous images, interpolation circuitry for mapping the result surface into x- and y-coordinates, and an interface with a device using the chip, such as a hand-held scanner.
The filter circuitry, the compression circuitry, the correlation circuitry and the interpolation circuitry are all embodied in an on-chip digital signal processor (DSP). The DSP embodiment allows precise algorithmic processing of the digitized signal with almost infinite hold time, depending on storage capability. The corresponding mathematical computations are thus no longer subject to the vagaries of CMOS chip structure processing analog signals. Parameters may also be programmed into the DSP's software making the chip tunable, as well as flexible and adaptable for different applications.
U.S. Pat. No. 5,644,139 to Allen et al discloses a scanning device and a method for forming a scanned electronic image including the use of navigation information that is acquired along with image data, and then rectifying the image data based upon the navigation and image information. The navigation information is obtained in frames. The differences between consecutive frames are detected and accumulated, and this accumulated displacement value is representative of a position of the scanning device relative to a reference. The image data is then positioned-tagged using the position data obtained from the accumulated displacement value. To avoid the accumulation of errors, the accumulated displacement value obtained from consecutive frames is updated by comparing a current frame with a much earlier frame stored in memory and using the resulting difference as the displacement from the earlier frame. These larger displacement steps are then accumulated to determine the relative position of the scanning device.
The above documents teach how to determine the position in a conceptual generation of navigation information. In this context the U.S. Pat. No. 5,927,872 to Yamada uses the navigation information for a hand-held scanner disclosed in U.S. Pat. No. 5,644,139 to Allen et al. The invention according to Allen et al teaches navigation through comparison of pixels on a frame basis.
When printing lines/rows of text or images with, for example, a hand held printer of a type described through the Swedish patent application 0102542-3 by Walling, not yet published but described below, there are problems related to skew between successive lines/rows, when the print-head is moved back and forth from the right to the left downwards on a print medium such as a piece of paper. The printing operation builds up an image of horizontal bands in lines where a lower band is an extension of an upper band. Hereby, sensor means for positioning sensing of the print-head are providing the printer with information so that positions and an angle of rotation can be determined on the print medium used. This must be accomplished very accurate in order to avoid skewing and/or clipping of, for example, printed characters.
Hence, if the absolute position and/or angle of rotation do not correspond with the values input to the printer, due to, i.a., the system resolution, the bands of text would not fit to each other. Obvious consequences of band skew are clipping/cutting of characters to be printed, depicted as a part of, for example, a character being printed in an upper band and the remaining part in a lower band in sweeps with the printer, and the character or word printed becomes hard to interpret, i.e., readability is distorted.
Regarding the resolution of a positioning sensor, currently used sensors have been shown to transfer mal positioning within 0.5–1.0%. In order to avoid distortion, current sensor resolution has to be improved with a factor 10.